Response Surface Methodology, an approach to predict the effects of a lactoperoxidase system, Nisin, alone or in combination, on Listeria monocytogenes in skim milk

Authors


Dr J.-B. Millière, ENSAIA-INPL, Laboratoire de Fermentations et Bioconversions Industrielles, 2, avenue de la Forêt de Haye, 54500 Vandoeuvre-les-Nancy, France (e-mail: milliere@iutnb.u-nancy.fr).

Abstract

Experimental designs using Response Surface Methodology (RSM) were used to determine effects and interactions of Nisin (0–200 IU ml−1), pH values (5·4–6·6), incubation time (0–36 h or 0–144 h) and the lactoperoxidase-thiocyanate-hydrogen peroxide system (LPS) on Listeria monocytogenes CIP 82110 in skim milk, at 25 °C. The LPS varied from level 0–2; LPS at level 1 consisted of lactoperoxidase (35 mg l−1), thiocyanate (25 mg l−1) and H2O2, which was supplied exogenously by glucose-oxidase (1 mg l−1) and glucose (0·2 g l−1); LPS activity was dependent on LPS level and incubation time. In the presence of LPS at level 1, a bacteriostatic phase was followed by growth, whereas at a higher level, a bactericidic phase was observed. Nisin response was time- and pH-dependent. Nisin was bactericidic at acidic pH values and for a short incubation time (12 h) only; then, a re-growth phase was observed. Nisin and LPS in combination gave an original response which lacked the transitory bactericidal effect of Nisin and had a continuously bactericidal affect, leading to 10 cfu ml−1 of L. monocytogenes at 144 h; the response was greatly affected by incubation time. Predicted values were in good agreement with experimental values. Response Surface Methodology is a useful experimental approach for rapid testing of the effects of inhibitors.

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